Tunnel furnace



NOV. 4, 1969 BUCHKREMER v 3,476,369

TUNNEL FURNACE Filed Aug. 14, 1967 V In van for: mac Jaw" Mame/75A Int. Cl. F27b 9/50, 13/02, 1/02 U.S. Cl. 263-36 6 Claims ABSTRACT OF THE DISCLOSURE A tunnel furnace which permits differing gas atmospheres within its furnace space, primarily for sintering soft ferrites, which includes sheet metal plates distributed over the length of the furnace, spaced from one another in the longitudinal direction of the furnace and extending transversely thereto, whereby the sheet metal plates are inserted on all sides into the brickwork of the furnace and are impervious to gas except for the channel aperture provided in the plates for the furnace channel. Additionally, gas supply and discharge lines for establishing a predetermined gas atmosphere within a given section defined between two plates terminate in the furnace channel within a given section.

Background of the invention The present invention relates to a tunnel furnace, and more particularly to a tunnel furnace for sintering soft ferrites.

For sintering soft ferrites in tunnel furnaces, differing gas atmospheres are required within the individual zones or regions of the furnace which have to be composed depending on the type of ferrite to be sintered. For example, there exists the requirement in many cases to produce an atmosphere rich in oxygen within the heatingup zone. On the other hand, there are also cases which require a differing oxygen content in different temperature areas within the heating-up zone. A reduced, constant or also decreasing oxygen content should exist within the zone of maximum temperature. A certain special curve of the oxygen content is required Within the cooling zone in relation to the cooling curve, according to which the highest purity of oxygen with the highest content of nitrogen or another inert gas is to be present within the largest part of the cooling zone. Hence, the requirement essentially consists in enabling always to so reproduce the curves of the atmospheric and temperature values prevailing within the tunnel furnace along its extent as required by the type of ferrite to be sintered.

Summary of the invention The basic underlying idea of the present invention is therefore to so construct a tunnel furnace having a varying gas atmosphere in the furnace chamber along its longitudinal extent and mainly intended for sintering soft ferrites, that any desired gas atmosphere, especially oxygen atmosphere, can be produced and maintained within the tunnel furnace at any desired places along its longitudinal dimension or extent.

The aim of maintaining a predetermined gas atmosphere within a predetermined section of the tunnel furnace is achieved according to the present invention in that sheet metal plates or screens, distributed over the length of the furnace, are inserted with mutual spacing transversely to the longitudinal direction of the tunnel furnace into the brickwork thereof and that these sheet metal plates or screens are impervious to gases except for the aperture of the furnace channel. Preferably these United States Patent sheet metal plates or screens extend through the entire brickwork.

In order to createa predetermined gas atmosphere at certain places of the tunnel furnace, it is recommended according to the present invention to have inlet and outlet lines for the gases terminate in the furnace channel between the sheet metal plates. In order that a desired gas atmosphere can both be produced as well as maintained at preselected places of the tunnel furnace, both aforementioned measures are utilized simultaneously according to the present invention. Sheet metal plates distributed over the length of the tunnel furnace and with mutual spacing are then inserted into the brickwork transversely to the longitudinal direction of the tunnel fur nace whereby these sheet metal plates are impervious except for the aperture forming the furnace channel and extend through the brickwork completely on all sides. Additionally, supply and discharge lines for supplying and discharging gases are provided between the sheet metal plates.

If, with a tunnel furnace constructed in such a manner, the ferrites are so stacked on ceramic plates or trays or carts lined with bricks that they fill uniformly the inner cross section of the furnace channel, then it is prevented with certainty by the measures of the present invention that gas flows from within the furnace brickwork which leads to a more or less large equalization of the furnace atmosphere in the different zones of the tunnel furnace. It is above all prevented with certainty that gas can reach from the chambers defined by the sheet metal plates by way of the brickwork of the tunnel furnace into the adjacent furnace area or section. Consequently, with a normal furnace construction according to the present invention, a pronounced oxygen decrease between two furnace regions may be realized over a short furnace length even if the oxygen content is to change, not gradually, but in a jump-like manner.

According to the present invention the furnace is subdivided, so to speak, into individual chambers in that gas-tight sheet metal screens extend through the entire brickwork from the outer sheet metal case of the tunnel furnace to the open channel. These sheet metal screens prevent practically any diffusion of the furnace gases in the direction of the furnace channel through the brickwork. The more such sheet metal screens are arranged at the places where the atmosphere is to change within the tunnel furnace, the more readily one is able to achieve a desired curve of the atmosphere and the less one needs to worry about an impairment of the desired curve configuration by flows within the brickwork.

A predetermined oxygen atmosphere may be established within the area between two sheet metal plates and may be maintained constant if gas supply and discharge lines are provided which terminate within the portion of the furnace channel disposed within a respective chamber. The gas atmosphere can then be regulated or adjusted to the desired extent by way of these lines.

Accordingly, it is an object of the present invention to provide a tunnel furnace of the type described above which eliminates the aforementioned shortcomings and drawbacks encountered with the prior art constructions.

It is another object of the present invention to provide a tunnel furnace, particularly for sintering soft ferrites which permits the ready establishment of differing gas atmospheres within different zones of the furnace.

A further object of the present invention resides in a tunnel furnace of the type described above which mini mizes the danger of equalization between the various sections of the furnace due to gas flows.

These and other objects, features, and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, one embodiment in accordance with the present invention and wherein:

FIGURE 1 is a side elevational view of a tunnel furnace according to the present invention;

FIGURE 2 is a partial longitudinal cross-sectional view, on an enlarged scale, illustrating the section of the tunnel furnace between lines IIH of FIGURE 1;

FIGURE 3 is a transverse cross-sectional view taken along line III-III of FIGURE 2; and

FIGURE 4 is a partial longitudinal cross-sectional view, on an enlarged scale, illustrating the section of the tunnel furnace between lines IV-IV of FIGURE 1, and depicting the brickwork thereof.

Referring now to the drawing wherein like reference numerals are used throughout the various views to designate like parts, reference numeral 1 generally designates the tunnel furnace according to the present invention which is provided with a furnace channel 2 within the brickwork 3 which, in turn, is surrounded by the sheet metal housing or sleeve 4. Sheet metal screens or sheet metal plates 5 extend through the tunnel furnace 1 at right angle to the furnace channel 2 whereby the sheet metal screens 5 are practically gas-tight and are provided exclusively with a passage aperture 6 corresponding in its internal dimensions with the dimensions of the oven channel. The sheet metal plates 5 are arranged distributed over the length of the furnace and are provided in particular in those places in which the configuration of the atmosphere curve is to change.

Two such sheet metal plates 5 are indicated in dash lines 5a and 5b in FIGURE 1. The remaining sheet metal plates 5 are not indicated in FIGURE 1 in order not to impair the clarity of the drawing. Two gas lines 8 and 9 lead into the section 7 defined by the sheet metal plates" 5a and 5b which discharge in the furnace channel 2. Gas may be supplied into the section 7 by way of one of the lines 8 and 9 and the gas mixture may be withdrawn from the furnace by way of the other line. It is possible in this manner to create within the section 7 of the tunnel furnace 1 a gas atmosphere which differs completely from the gas atmosphere in the adjoining furnace spaces 10 and 11. The gas composition present in section 7 then also remains preserved in this section because the sheet metal plates 5 prevent the passage of gas within the brickwork 3 from the section 7 into the furnace spaces 10 and 11 as well as the passage of gases out of the furnace spaces 10 and 11 into the section 7. Consequently, the diffusion within the brickwork 3 is effectively prevented. Thus, at preselected places of the tunnel furnace a desired oxygen atmosphere may be established and kept constant without diffculty in that the necessary protective gas is supplied and the exhaust gas is conducted off. By reason of the fact that the sheet metal plates 5 are arranged distributed over the entire length of the tunnel furnace, a large number of sections 7 results which brings about that a desired gas atmosphere can be produced in all of these sections and can be maintained during operation of the tunnel furnace.

While I have shown and described only one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to a person skilled in the art, and I therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

I claim:

1. A tunnel furnace having wall means defining a longitudinal channel therein, wherein the wall means are at least partially pervious to gas, which comprises,

a plurality of substantially completely gas impervious metal plate means disposed at spaced intervals along the length of said channel and substantially transverse thereto to define a plurality of adjoining treating zones, each of said plate means having an aperture therethrough corresponding to the crosssectional shape of said channel and communicating therewith to provide access between adjoining zones, said plate means being inserted into said furnace walls to substantially completely preclude the diffusion of gas between adjoining zones except through the apertures in said plate means.

2. A tunnel furnace as defined in claim 1 wherein inlet and outlet means communicate with said channel in each of said treating zones for introducing and withdrawing the atmosphere therein.

3. A tunnel furnace as defined in claim 2, wherein said plate means extend substantially completely through said wall means on all sides.

4. A tunnel furnace as defined in claim 3, wherein said wall means comprises a brickwork.

5. A tunnel furnace as defined in claim 1, wherein said wall means comprises a brickwork.

6. A tunnel furnace, primarily for sintering soft ferrites, having varying gas atmospheres within the furnace and along the length thereof, which comprises:

a brickwork defining a longitudinal furnace channel,

a plurality of substantially completely gas impervious sheet metal plates disposed at spaced intervals along the length of said channel and substantially transverse thereto to compartmentalize the furnace into a plurality of treating zones, each of said plates having an aperture therethrough corresponding to said channel and communicating therewith, each of said plates extending substantially through said brick work on all sides to substantially completely preclude diffusion of gas between adjoining zones except through said plate apertures;

a gas supply line provided in each treating zone for introducing a controlled atmosphere therein; and

a gas discharge line provided in each treating zone for withdrawing the atmosphere therefrom.

References Cited UNITED STATES PATENTS 1,828,669 10/1931 Kulzinsk.

3,189,336 6/1965 Montagino 263--36 3,415,503 12/1968 Beck 2638 JOHN J. CAMBY, Primary Examiner US. Cl. X.R. 

